Autodesk Meshmixer for Windows

https://meshmixer.org/

Autodesk Meshmixer is a free, powerful, and lightweight software designed for editing, repairing, and manipulating 3D triangle meshes (STL, OBJ, PLY) for 3D printing, scanning, and digital sculpting. It excels at "mesh surgery" tasks like hollowing, adding support structures, cutting, and combining models, acting as a critical, user-friendly tool for prepping designs.